Make sure to look carefully at corner cases, like max-load at
min-input-voltage (typically causes max inductor current).
>From the app-note, I see there is a discrete NMOS transistor, and
thankfully a single inductor (not transformer), so your modeling is easier.
Be very careful about the voltage spikes across the NMOS device; you must
never allow Vds to exceed the max-spec value, which often derates at
There are a lot of devices with low Rds(on); when I say low, I'm talking
below 50milliohms, but they often have higher gate-source capacitance and
require higher gate-drive voltage. This will put some constraints on the
gate-driver. So, tradeoffs need to be made. I'd suggest picking a device
with a low-enough Rds(on) such that it's power-dissipation does not cause
significant heat-rise with a small heat-sink.
Using the tiny PCB-mounted devices is tricky for thermal reasons; I prefer
TO-220 packages or similar.
There's a lot of really good info in the TI datasheet, appnote, and the
IRF7807 datasheet. Once you read thru all of that you will have a good
understanding. Just be aware the IRF7807 wont give you nixie-level voltages
as t's rated for 30V max.
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